As labor-saving means for a reinforcing bar binding work, there is an electrically-driven reinforcing bar binding machine for winding a wire around reinforcing bars to bind these reinforcing bars together. One kind of reinforcing bar binding machine is provided with a wire feed mechanism, a wire cutting mechanism, and a wire twisting mechanism, and a wire is fed along a guide nose of a curved shape by the wire feed mechanism, so that reinforcing bars are surrounded by a wire loop, and the wire loop is cut off from the wire extending from a trailing end of the wire loop by the wire cutting mechanism, and at the same time the wire loop is twisted by the wire twisting mechanism to bind the reinforcing bars in closely contacted relation thereto.
The wire feed mechanism employs a pair of V-grooved gears disposed in mesh with each other, and one of the V-grooved gears is driven by a motor, and the other V-grooved gear of a follower type is resiliently contacted with the one V-grooved gear such that the wire is held between the two V-grooved gears, and these V-grooved gears are driven for rotation so as to feed the wire (JP-A-2003-054511, JP-A-2003-267307, etc.). The amount of feed of the wire is controlled on the basis of a number of revolutions of a feed motor or the V-grooved gears, and is set, for example, to an amount corresponding to 4 turns plus α, and each time a trigger lever is pulled, the wire is fed in an amount corresponding to 4 turns plus α (which amount is equal to 3 turns around the reinforcing bars plus an additional amount for binding purposes), thereby effecting one cycle of binding operation.
In the above reinforcing bar binding machine, the number of turns of the wire around the reinforcing bars is set to a preset value, but there are those binding portions on which a large load and stresses will not act, and therefore do not require a large binding force. To provide a multiplicity of turns of the wire at such binding portions leads to waste of the wire. Also, there is a case where it is desired to effect the binding with a force larger than a preset binding force; however, when a twisting torque is increased while using the preset number of turns, the wire is twisted off, and therefore it is necessary to increase the number of turns. Furthermore, it may be proposed to apply the reinforcing bar binding machine to other uses than the binding of reinforcing bars, such for example as the binding of resin-made pipes for electric wiring and the binding of hot water heating pipes. However, a binding force required for the pipes of this kind is not so large as the binding force required for the reinforcing bars, and when the wire is wound in a multiplicity of turns as is the case with the reinforcing bars, this leads to waste of the wire, and besides there is a fear that the pipes are broken with a large binding force.